Scanning laser SQUID microscopy is known as a method of non-destructive inspection of a sample such as a semiconductor wafer. With a scanning laser SQUID microscope, the area of a defect or a related location is irradiated with a laser. At such time a current flows, a magnetic field induced by the current is detected by a SQUID fluxmeter and an image is obtained by scanning either the laser or the sample (see Non-Patent Document 1). When a semiconductor substrate serving as the sample is irradiated with a laser beam, a pair consisting of an electron and positive hole generated by irradiation with the laser beam becomes an electric current owing to an electric field at a p-n junction, etc. This current is referred to as an OBIC (Optical Beam Induced Current). Alternatively, when heating occurs owing to irradiation with a laser beam, a temperature gradient produced by a defect or the like develops an imbalance and a current flows owing to the thermoelectric effect (see Non-Patent Document 1 and Patent Document 1).
It should be noted that Patent Document 2 discloses a non-destructive inspection apparatus for scanning a sample by moving the position on a sample that is irradiated with laser light, detecting a magnetic field, which is produced by scanning of the sample, using a SQUID fluxmeter, acquiring magnetic-field distribution data, subtracting the magnetic-field distribution data from standard distribution data or vice versa to thereby produce difference data, comparing the difference data with a positive first threshold value and a negative threshold value, determining that a defect of a first type exists at the laser-irradiated position when the difference data is greater than the first threshold value, and determining that a defect of a second type exists at the laser-irradiated position when the difference data is less than the second threshold value.
[Patent Document 1]
Japanese Patent Kokai Publication No. JP-P2002-313859A
[Patent Document 2]
Japanese Patent Kokai Publication JP-P2004-93211A
[Non-Patent Document 1]
K. Nikawa, S. Inoue, “Novel Nondestructive and Non-contact Failure Analysis and Process Monitoring Technique—Scanning Laser-SQUID Microscopy—”, LSI Testing Symposium/2000 Conference (H12.11.9-10), pp. 203-208
[Non-Patent Document 2]
Bradley J. Roth, Nestor G. Sepulveda and John P. Wikswo, Jr., “Using a magnetometer to image a two-dimensional current distribution” J. Appl. Phys., 65(1), 1 Jan. 1989